This invention is directed to a method of converting an oxygenate to an olefin product, particularly ethylene, propylene, and butylene, using a silicoaluminophosphate molecular sieve catalyst.
Ethylene is an important petrochemical. In 1998 about 80 million tons of ethylene were produced, and demand is expected to reach 100 million tons by 2003. The primary use for ethylene is as a monomer for the production of low and high density polyethylene. Approximately 60% of world ethylene consumption goes into making polyethylene for such products as plastic films, containers, and coatings. Other uses include the production of vinyl chloride, ethylene oxide, ethylbenzene and alcohols.
Propylene is another important raw material. In 1998 about 46 million tons of propylene were produced, and demand is expected to reach 60 million tons by 2003. About 55% of the world consumption is directed to the production of polypropylene. Other important end products include acrylonitrile for acrylic and nylon fibers, and propylene oxide for polyurethane foams.
Butylenes are useful in preparing a wide variety of derivative end products. Examples of such end products include gasoline alkylate and ethylene-butylene (EB) copolymer. Butylenes are also used as chemical building blocks for larger hydrocarbons. These hydrocarbons find such applications in fuels, lubricants, and specialty chemicals, e.g., plasticizers and solvents.
Ethylene, propylene, and butylene have been traditionally produced by either catalytic or steam cracking of a petroleum feedstock. As the cost of petroleum steadily increases it will be important to find alternative feedstock sources for producing these olefins. Oxygenates are a potential useful alternative to petroleum for producing ethylene and propylene. A particularly promising oxygenate is methanol. Methanol is readily produced from synthesis gas, which is derived from the reforming of natural gas. Large scale production of methanol from xe2x80x9cstrandedxe2x80x9d natural gas could provide methanol at a price that would allow methanol to be economically competitive with petroleum feedstock for the production of ethylene and propylene.
One way in which olefins can be made from an oxygenate feedstock is by catalytic conversion. In U.S. Pat. No. 4,499,327 a catalytic process for converting methanol to olefins is described. The catalyst used in that process contains a silicoaluminophosphate molecular sieve.
It is highly desirable to convert as much of the oxygenate feedstock as possible into as much olefin product as possible. Various methods of doing such have been suggested. For example, U.S. Pat. No. 4,677,242 describes a method of increasing the amount of ethylene and propylene produced from the catalytic conversion of methanol by adding an aromatic diluent to the methanol. The catalyst that is used in the process contains a silicoaluminophosphate molecular sieve. The use of the diluent is said to result in an increase ethylene selectivity. U.S. Pat. No. 4,499,314 also discloses a catalytic process for converting methanol to ethylene and para-xylene. The catalyst that is used is a zeolitic molecular sieve, ZSM-5. Promoters are used to promote either the formation of aromatic products or olefin products. Benzene, toluene and para-xylene are preferred aromatic promoters. Ethylene, propylene and butenes are preferred olefin promoters.
Silicoaluminophosphate molecular sieve catalysts are particularly useful catalysts for making olefins, such as ethylene and propylene, from oxygenate compounds, such as methanol. However, improved process conditions are needed to increase the production of ethylene andlor propylene, as well as butylene if an oxygenate feedstock is to replace or supplement petroleum feedstock for the production of these olefins. Also, because of market demand fluctuations for ethylene, propylene, and butylene, it would be desirable to vary the production ratio of ethylene to propylene to butylene without significant downtime in production.
The invention is directed to a method for increasing ethylene, propylene, and/or butylene production in an oxygenate to olefin process using molecular sieve catalysts. Catalyst from the regeneration zone, and optionally fresh catalyst, is contacted with an alcohol in an alcohol contact zone prior to contacting the regenerated or fresh catalyst with the oxygenate feedstock. The alcohol is selected from methanol, ethanol, 1-propanol, 1-butanol, or a mixture thereof. The alcohol or mixture of alcohols used in the alcohol contact zone will affect the production ratio of ethylene to propylene to butylene in the olefin product.
The method for increasing ethylene, propylene, and/or butylene production in an oxygenate to olefin process includes contacting a molecular sieve catalyst with an oxygenate, preferably methanol, to convert a portion of the oxygenate to an olefin product; separating the catalyst from the olefin product and directing a portion of the separated catalyst to a regenerator; contacting, in an alcohol contact zone, the regenerated catalyst with an alcohol, selected from the group consisting of ethanol, 1-propanol, 1-butanol and mixtures thereof; and directing the alcohol contacted catalyst from the alcohol contact zone to an oxygenate conversion zone. The method may further include separating hydrocarbon produced in the alcohol contact zone from the alcohol contacted catalyst, and adding fresh catalyst to the alcohol contact zone. The molecular sieve catalyst used in the invention contains SAPO molecular sieve selected from SAPO-5, SAPO-17, SAPO-18, SAPO-20, SAPO-34, SAPO44, SAPO-56, the metal containing forms of each thereof, or mixtures thereof. Desirably, the temperature of the alcohol contact zone will be about 350xc2x0 C. to about 550xc2x0 C. Preferably, the alcohol contact zone is an auxiliary reactor.
The present invention will be better understood by reference to the Detailed Description of the Invention when taken together with the attached drawings and the appended claims.